Plays a background music phrase through the ZX Spectrum beeper. Reads the music-active flag at 33737. If zero, falls through to the fixed ~36 ms delay at BusyWait and returns — the idle main loop therefore pays this wait TWICE per iteration (here and in FrameTiming). Otherwise plays a descending sequence of tones: reads 32 consecutive ROM bytes from $0200 and for each byte toggles bit 4 of port $FE (beeper output), with a delay of C counts between toggles. After each 32-byte block, decrements C by 8 to raise the pitch, producing a descending arpeggio effect. Runs until C underflows (B=255 exhausted), then returns.

Used by the routines at 36457 and 43242.